Currently, the number of networks around the world is growing at a faster and faster pace. In addition to new networks being installed existing networks are being upgraded and expanded as companies increase in size and more and more users are added to internal networks. Enterprise networks are presently enjoying a huge increase is popularity with thousands of new nodes and users being added each week. The increased number of users is forcing these enterprise network administrators to add more equipment to meet surging demand and is also forcing the bandwidth capabilities of the enterprise network to increase both in terms of new communication links being added and slow speed links being upgraded to higher bandwidth links.
The use of multicast messages for point to multipoint communications is expected to help alleviate congestion and reduce bandwidth consumption on most enterprise networks in the future. Presently, its use is limited as much of the equipment, i.e., routers etc., that is in use on enterprise networks does not support the new multicast protocols. Eventually, the use of multicast protocols on enterprise networks, will significantly reduce the traffic required to be sent for point to multipoint type communications.
Further, scaleable switching technology has enabled the construction of large switched networks. Broadcast traffic forwarding, however, does not scale well in large networks because all the network hosts are exposed to broadcasts from all other hosts. In other words, in level 2 networks, i.e., networks operating at the link layer in the ISO communication stack, large portions of bandwidth are wasted as each node on the level 2 network receives all multicast traffic. Under normal conditions, multicast traffic is flooded to all stations on the network, thus degrading performance. A suitably configured router (level 3 device) functions to filter the multicast traffic and only forward it to network segments that should receive it. Absent a router or other level 3 filtering, however, each node or workstation on the level 2 network will receive all multicast traffic. Thus, the filtering is performed at each station that receives multicast messages.
Prior art attempts at reducing bandwidth waste in connection with multicast traffic include assigning filters within level 2 switches that function to scan and filters the content of every frame that is received. This requires more complicated hardware and/or software content within the switch which drives up its cost significantly.
In addition, in response to the broadcast traffic flooding problem described above, VLANs can be used to partition the broadcasts into domains that permit the switched network to keep growing. Since it is common nowadays to connect network ports to the switched infrastructure rather than routers or servers, the logical partition of the network no longer directly effects the configuration of higher layer devices. Thus, network administrators can more easily assign and reassign network regions to logical groups without expensive reconfiguration of the host, router or server.
Typically, Media Access Control (MAC) layer multicast messages are forwarded according to the VLAN broadcast data path. However, while broadcast forwarding is usually related to address resolution/SAP) location type administrative traffic, the nature of multicast traffic is usually very different. Multicast traffic, especially IP multicast traffic is typically associated with particular types of application such as video broadcasting and video conferencing. These applications are typically characterized by: (1) setup of a group communication session (2) high traffic volume and (3) the crossing of VLAN boundaries that were previously setup for subnetting purposes.
In addition, conventional VLAN capable network devices are not capable of containing multicast traffic flooding since all regular members of the VLAN will hear multicast traffic. Further, the implementation of the VLAN itself is vendor specific. For example, some implementations are port based while others are based on other criteria.